A method for removing oxide contamination from titanium diboride powder involves the direct chemical treatment of TiB2 powders with a gaseous boron halide, such as bcl3, at temperatures in the range of 500°-800°C The bcl3 reacts with the oxides to form volatile species which are removed by the bcl3 exit stream.
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1. A method for purifying titanium diboride powder contaminated with an oxide selected from the group consisting of TiO2, Ti2 O3, Al2 O3, SiO2, and B2 O3, comprising:
contacting the contaminated titanium diboride powder with an excess amount of gaseous bcl3 to thereby form gaseous (BOCl)3 by reaction of said bcl3 with said oxide; and separating the gaseous (BOCl)3 from the titanium diboride powder.
2. The method of
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This invention, which was made under a contract with the U.S. Department of Energy, relates to titanium diboride powder and, more particularly, to a method for purifying such powder.
Titanium diboride (TiB2), an extremely hard refractory solid with very high resistance to oxidation and very low electrical resistance, is commonly commercially produced by the carbothermic reduction of a mixture of the oxides of titanium and boron. The TiB2 product from this process is always contaminated with oxides. Another method for producing TiB2 involves chemical vapor deposition from a mixture of titanium tetrachloride (TiCl4), boron trichloride (BCl3), and hydrogen (H2) on a hot surface. This method produces macrosize crystals of pure TiB2 which must be mechanically ground into powder and which consequently become contaminated, usually with metal oxides (Al2 O3,SiO2) from the grinding apparatus. It is suspected that this oxide contamination has a deleterious effect on the sintering of the powders and furthermore on integrity of sintered products.
Modifications to existing processes that would result in the direct production of pure TiB2 powders could be costly. It is therefore desirable to have a method for removing oxide contamination from TiB2 powders produced by existing processes.
It is the object of this invention to provide a method whereby oxide contamination can be removed from TiB2 powders. This is accomplished by chemically treating TiB2 powders with a gaseous boron halide such as boron trichloride (BCl3) at temperatures in the range of 500°-800°C The BCl3 reacts with the contained oxides to form volatile species which are removed by the BCl3 exit stream. Typical reactions, depending on which oxides are present, are represented by the following equations: ##STR1##
Equilibrium constants for the above equations show favorable values at 1000K indicating that all of the reactions are spontaneously effective. Thus, the oxide-contaminated TiB2 obtained from the aforementioned commercial processes can readily be purified by treating the product with BCl3 in accordance with the method of the invention.
A number of 1.25 g samples of commercially available TiB2 were treated with BCl3 at temperatures in the range of 500°C to 850°C Each sample was analyzed for oxygen content and placed in a gold combustion boat. The boat was inserted into a nickel tube which had been passivated by a pretreatment with BCl3. A flow of BCl3 (40 ml/min.) was directed through the tube as the tube and sample were heated to the desired temperature by a tube furnace. Each sample was treated for two hours and then cooled to room temperature in an argon atmosphere. The system was then transferred to a glove box with an inert atmosphere for weighing and sampling the TiB2. Oxide content of the samples was based on the oxygen content as determined by neutron activation analysis (NAA). Results are shown in Table I below.
TABLE I |
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% Oxygen (by NAA) Temperature |
As received After BCl3 Treatment |
°C. |
______________________________________ |
4.1 0.68 850 |
0.75 0.57 850 |
4.1 1.5 500 |
4.2 1.5 600 |
4.2 1.3 700 |
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A second group of samples of TiB2 of the same size and origin used in Example I was exposed to BCl3 at temperatures ranging from 600°C to 800°C Each sample was placed in a previously BCl3 -passivated vertical nickel tube equipped with a nickel frit at its bottom end to retain the TiB2 and allow passage of BCl3. As the system was heated under argon to a desired temperature, a flow of BCl3 (40 ml/min.) was directed upward into the bottom of the tube and through the nickel frit. The particles of TiB2 were dispersed and suspended in the flowing BCl3, providing an improved solid-to-gas contact. Each sample was treated at a specific temperature for four hours and then processed according to the cooling, weighing, sampling, and analyzing procedure of Example I. Results are shown in Table II.
TABLE II |
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% Oxygen (by NAA) Temperature |
As received After BCl3 Treatment |
°C. |
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4.2 1.7 700 |
4.2 1.3 600 |
0.58 0.37 650 |
1.7 0.3 650 |
2.2 0.8 650 |
2.0 0.8 650 |
0.8 0.64 800 |
2.7 0.63 700 |
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Bamberger, Carlos E., Brynestad, Jorulf
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Apr 12 1983 | BAMBERGER, CARLOS E | UNITED STATES OF AMERICA AS REPRESENTED BY THE SECRETARY OF THE DOE | ASSIGNMENT OF ASSIGNORS INTEREST | 004145 | /0764 | |
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